This invention relates generally to a coupler for a screw clamping device provided for the opening and closing of pressure vessels, and more particularly to such a coupler which includes a pair of opposing clamping jaws having grooved inner walls engageable with annular grooves provided on an elongated bolt which holds down a cover onto the pressure vessel. Both clamping jaws are actuated by a single pressure-operated piston and cylinder unit.
In known couplers provided to facilitate the opening and closing of pressure vessels, opposed clamping jaws must be moved separately into and out of clamping engagement with an elongated bolt provided for securing the cover to the pressure vessel. Independent movement of each clamping jaw is carried out by means of separate pneumatically operated piston and cylinder units as disclosed in German Patent No. 1,300,467, commonly owned herewith. Such an arrangement, however, is relatively complex, is somewhat cumbersome to operate and is basically uneconomical. The terminal clamping and unclamping positions of the jaws, in accordance with the prior art, must be carefully monitored by means of, for example, electric terminal switches, light switches or pneumatic sensors for ensuring the fully clamping and unclamped positions of the jaws. Such monitoring devices, which are costly and cumbersome, were required to coincide the terminal ends of the clamping and unclamping positions with that of the monitoring function.